The L12 mod I believe is only for 266fsb default chips to make them into 333fsb default. His Barton 2500+ is already a 333fsb chip, so it wouldn't do anything for him. I have heard things about some other mod that makes it a 400fsb default, but doesn't add anything to fsb walls, since the boards really only seem to increase their fsb capabilities drastically when going from 266->333fsb default chips.
Other than that what everyone has mentioned already (particularly vdd mod), the only thing you may want to try is lowering your vdd voltage. It sounds counter-intuitive, but there were a few cases at the EO forums I believe where at higher fsbs, (230's...), a vdd of 1.4 or 1.5 was more stable than 1.6 or 1.7. It's not the case with my board, but there were enough cases of it that it's a possibility. Couldn't hurt to try.... Other than that, you've probably just hit your fsb wall, and without some volt mods, there's no easy way to get more fsb.
As 9mm said though, I'd definitely work on getting that cpu mhz higher (ie. spend your money/time getting better cpu cooling
). Mem bandwidth is nice and all, but one might even say it's a *little* overrated. A higher cpu speed will give a far more noticeable and meaningful performance increase than a little higher fsb/mem bandwidth.